Template assisted synthesis of nanocrystalline sulfated titania: active and robust catalyst for regioselective ring opening of epoxide with aniline and kinetic modeling

Abstract

The regioselective ring opening of epoxides with aniline affording β-amino alcohols is commercially important. A variety of heterogeneous catalysts such as fuel lean sulfated zirconia (FLSZ), UDCaT-5, 20%Cs_2.5H_0.5PW₁₂/K-10 clay, Hβ-zeolite, nanocrystalline sulfated titania (NCST), and titania were evaluated in the reaction of epichlorohydrin with aniline. A nanocrystalline sulfated titania (NCST) catalyst, the most active and selective, was prepared by the sol–gel method using poly(vinyl alcohol) (PVA) as a green template and functionalized using sulfuric acid. The sulfate content was in the range 4.1% (w/w). It was well characterized using TEM, FT-IR, XRD, NH₃-TPD, N₂-BET surface area, and TGA. The effects of various parameters such as speed of agitation, molar ratio, catalyst loading, and temperature using the NCST catalyst were investigated in the reaction of epichlorohydrin with aniline to achieve good yields and excellent regioselectivity at 60 °C and 0.01 g/cm³ catalyst loading. The catalyst was effectively recycled for five consecutive cycles without any significant loss in its activity. Furthermore, a reaction mechanism was proposed to deduce a kinetic model which was validated against experimental data. The entire process is green. The protocol was extended to the reaction of several epoxides and amines over NCST to make corresponding β-amino alcohols.